This invention relates, in general, to shaft seals and bearings for a rotatable shaft disposed within a casing. In particular, this invention relates to a butterfly valve construction.
Butterfly valves used for controlling the flow of steam into a modern steam turbine is a relatively new application of an old well-known device. However, the introduction of the butterfly valve into steam turbine technology requires improvements not found in the prior art due to relatively high steam temperatures and pressures coupled with control system requirements that the valve be highly reliable and fast-closing. Moreover, in the case wherein the steam generator is a nuclear reactor, it is required that there be no steam leakage from the valve because of possible radioactive contamination.
One possible steam leakage path out of the valve casing is axial steam leakage along each shaft end and the valve casing portion wherein each shaft end is rotatably supported. Further complicating the steam leakage problem is shaft flexure or bending caused by the high-pressure steam flow. The occurrence of shaft flexure may further aggravate the problem of shaft leakage while contributing to binding between the shaft and shaft seals.
It is therefore the object of the present invention to provide a highly reliable, fast-closing butterfly valve wherein the leakage of controlled fluid along the valve disc shaft axis, out of the valve casing, is eliminated under conditions of high steam pressure and shaft flexure.